The invention concerns a roll, preferably a paper machine press roll, which together with a backing roll forms a press gap, and which features a tempering device. A roll of this general type is known from DE-OS 27 06 850.
The tempering device provided in the interior of such a roll serves preferably to cool the roll shell, however it can also serve to supply heat to the roll shell. The known roll requires a cooling because it is part of a metal continuous casting system. Similar rolls serve as press rolls in papermaking machines. Here, a problem results from the fact that press rolls of that type are provided on their outer shell surface with an elastomer coating. During the roll operation together with the backing roll, heat occurs in the elastomer coating due to the inner flexing work of the elastomer taking place in the area of the press gap, which heat needs to be removed continuously. In this context, allowance must be made for the fact that rolls of that type are used in a 24-hour continuous operation and that in modern papermaking machines ever further increases of the operating speed and contact pressure are sought after.
In the prior rolls, the tempering device is of a design such that cold water flows along the inside circumference of the roll shell, absorbing heat and leaving the roll again at elevated temperature. The following problem occurs in the process: Conditioning the cooling water so that it will have the required low temperature and the purity necessary for continued operation causes high costs. As a further aggravation, the cooling water, despite careful conditioning, can chemically attack the inside surface of the roll shell in a nonpredictable way, due to its content of oxygen and/or aggressive ingredients (for instance humic acids). This may be the cause of oscillation crack corrosion and, following thereof, an unexpected break of the roll. On some prior rolls, this risk is avoided by using oil as cooling medium. However, the costs for conditioning the oil are still higher than those for conditioning of cooling water. Therefore, oil cooling pays only in rolls with adjustable flexure, where the oil can at the same time serve to transfer the press force from the roll shell to a fixed bending axle.
The problem underlying the invention is to advance a roll of the type described in such a way that the tempering (mainly the cooling) of the roll shell will be possible at an expense lower than before, and that in doing so the risk of oscillation crack corrosion will be avoided.